As has already been said, its personal choice but for me it would be Salou. I like Majorca as well but Salou has more the atmosphere I look for, its not as in your face as Magaluf but not as quiet as somewhere like Puerto Pollensa.
Agreed, some parts of Salou are looking tired, but this is more the northern end of the resort. The central and southern part of the resort are fine so this is the part I go to now, and I find no reason to go to the northern end.
So its Salou for me but if you haven't tried Majorca before then I'd be tempted to say give it a try, its the only way you'll know which you prefer. Salou will still be there next year!!
Just one thing though, Its hard to compare a resort to an entire Island - maybe if you decide what resort in Majorca you are considering it will be easier to do a true comparison.
Have a good holiday
Mark